Grinding mill



p 9 E. GERASCH 2,013,179

GRINDING MILL Filed Feb. 23, 1955 Fig.1

ERNST GERASCH ATTORNEY Patented Sept. 3, 1935 UNITED STATES PATENT OFFICE GRINDING MILL many Application February 23, 1933, Serial No. 658,158 In Germany March 1, 1932 3 Claims. (01. 83-9) My invention relates to grinding mills of the rotary drum and ball type for finely comminuting and pulverizing' solid materials in bulk, primarily hard substances such as minerals of difierent description including ore, coal, coke, etc.,also metallurgical, chemical and ceramic products, cement clinker and the likeand more particularly to improvements in grinding mills of the type composed of a plurality of individual grinding compartments or chambers so arranged around a common axis, as shown for instance in U. S. Patent 1,290,178 to Hachter and U. S. Patent 1,646,- 532 to Goebels, that the weight of the material and the grinding balls are more uniformly and symmetrically distributed within the mill, viz. on both sides of the central axis of the mill and will in part counterbalance each other with the result that less power is required for the operation of the mill. I have observed in the course of my experimental work with multiple chamber mills of various types including those described in the U. S. patents mentioned above, that the outstanding advantage of saving power, which in some cases amounts to 30% power saved in revolving the mill (see U. S. Patent 1,290,178 page 1 lines 38-49), is counterbalanced by more than one serious disadvantage which include the facts that the output of the mill is impaired, viz. being smaller than the output of mills of equal size, the rotary drum of which is not subdivided into a plurality of grinding chambers but presents one single chamber, and that the temperature to which the material under treatment rises in passing through the mill is higher than with mills of the single chamber type, an objectionable efiect for instance in grinding explosives, food stuffs etc.

I'have attempted to trace the cause of these drawbacks by taking photos of multiple chamber mills while working, the front walls of the.

chambers were made from wire net work or glass, through which the movement of the grinding elements could be observed in all the different phases of the circular movement of the grinding chambers.

As the result of my investigations I r ttribute the said drawbacks to the fact that the pieces of material to be ground are not appropriately hit by the falling grinding balls, viz. not in the most efiective manner at right angles perpendicularly from above, but underan'angle of impact or descent considerably' smaller than 90, with the result that the impact force of the falling grinding balls is not fully used for the comminution of the material, bu that a component of the impact force is consumed by an undesired motion of the material which laterally recedes under frictional contact with the supporting walls, whereby heat is produced. c

I have also found that the balls tend to obstruct the passage of the material entering the grinding chambers, thus impairing the working capacity of the mill, and that these drawbacks are the more noticeable the lighter the specific weight of the particular substance to be ground is 'in comparison to that of the material of which the grinding balls consist; in many casesas known to practitioners-the balls and the linings of the drum must be made of a special material, different from iron, and chosen according to the nature, viz. the physical and chemical properties of the substance to be ground, and also in accordance to the respective purpose for which the pulverized substance is intended, for instance manufacture of paints or of explosives, photographic, medicinal goods, food stuffs etc.

One of the primary objects of the invention is to overcome the said drawbacks by providing a grinding mill of the typeset forth and of im.- proved construction, the intake of the grinding chambers being so designed that the material to be ground will easily find its way into the mass of balls and underneath the latter.

In connection therewith the invention aims at so re-designing the grinding chambers that a uniform and speedy progress of the material to be ground through the latter and a greater output of the mill is obtained. 7

' Another object of the invention is to provide an improved mill of simple and sturdy construction the interior of the grinding chambers of which is readily accessible for supervision and repair, exchange of worn grinding balls, replacing of linings etc.

The nature and scope of the invention are briefly outlined in the appended claims and will be more fully understood by the following specification taken together with the accompanying drawing in which Fig. 1 is a longitudinal section through a mill designed according to this invention and being shown by way of an example,

Fig. 2 is a cross section on line I-I of Fig. 1, Fig. 3 is a cross section on line II--II of Fig. 1, Fig. 4 is a cross section on line III-III of Fig. 1,

Fig. 5 is a cross section through the ball section of the mill drawn' in a larger scale and elucidating the motion of the grinding balls in the different compartments of the mill during their circular movement.

In the embodiment of the invention shown by way of an example the ball mill, identified as a whole by letter B, comprises a drum in rotatably mounted in bearings ll, I2 of frame I! by means of hollow trunnions i4, i5-and being rotated by an electric motor' 16 and a toothed gearing l1. s

The interior of the drum ill is subdivided by partition walls 20 (Fig. 4) into a plurality of individual grinding chambers which are arranged around the central axis of the drum at the distance therefrom. The said partition walls 20 are plane and deviate from the radial direction so as to enclose with their central portion c (Fig. 1) a hollow space hereinafter called feed chamber".

Conveying means of appropriate design are provided at the front end of the mill B for charging the material to'beground into said feed chamber and thence into the grinding. chambers. Perforated screens, serving as intake means are provided in the central walls allowing the material to freely enter the grinding chambers and to find its way into the mass of grinding balls and underneath the latter, as will be seen hereinafter.

Protecting means are provided in the grinding chambers for keeping the grinding balls out of contact with the perforated screens, thus insuring an unobstructed flow of the material through the latter and preventing their becoming choked. In the embodiment of the invention, shown by way of an example in the drawing, tLe said protecting means comprise a hood structure formed with partition walls a, and a which enclose the perforated screen i from above and at its inner side, and leave a free passage for the material entering the grinding chambers; I prefer to provide in addition in said passage a grate u, the bars of which are at a distance from each other which is smaller than the--diameter of the balls or other gravitally controlled grinding elements used in the mill; in this'manner the intake screen i is rendered safe against injurious attacks from the balls and against being choked by the latter; and the material under treatment. Manholes closed'up by detachable lids 30 are provided in theputer walls of the grinding chambers so as to render accessible the interior of the latter for inspection and repair, exchange of worn balls for new ones, replacing of worn linings inside the mill etc. In the embodiment of my invention shown by way of an example at the feed end of the ball mill B another grinding mill A having a drum l0 and gravitally controlled rods 40 as grinding elements is arranged in structural and cooperative union with the ball section B of the mill; the rods 40 are carried. on and held together in bunches by systems of spokes 4|, 4| which extend tangentially to a central hole 42 in the spoke" structure of circular shape and form substantially triangular cages. As seen in the lower right (southeast by south) corner of Fig. 2 the rods 40 will periodically form a particularly high pile and bear against each other and the drum l0 with increased pressure, when lying in a certain wedge shaped portion of their triangular cages viz. that -which presents the smallest angle.

By arranging said spokes 4|, 4| in the specific tangential position described above and shown in Fig. 2 a very powerful comminuting effect is ,obtained from the rods 40,--wh ich is particularly useful for rapidly breaking up hard materials composed of coarse granular pieces.

The material to be ground, after having been broken up in the rod section A of the mill, passes through a perforated disk 45 into a receiver R. provided as a storage member between the sections A and B, and thence through openings 35' of a partition wall 35 onto substantially radially extending vanes or chutes 36 which are provided in the space between said partition wall and the front walls of the grinding chambers; on sliding down from the chutes the material to be reground in the ball section B of the mill arrives at a central chute member 36. wherefrom it slides into the feed chamber of the ball mill described above.

The feed chamber is closed up at its rear end by a partition wall 38 (Fig. 1).

The re-ground material-passes out of the ball mill B through a sieve plate 55 provided at the rear end of-the grinding chambers and is dis charged by radial chutes 55' into the hollow trunnion I 5.

Both trunnions l4, I! are provided at their inner faces with helical ribs used as conveying elements and being known per se.

Various changes and modifications in the design ci grinding mills of my improved construe tion having thefeatures described above may suggest themselves to practitioners in this field, without departing from the spirit and the salient ideas of this invention and sacrificing. any advantages obtained thereby.

For instance different intake and protecting means may be used in the ball section B of the mill:

Good results as regards fineness of the pulverized product and output of the mill perunit of power consumed have been obtained with a combined rod and ball mill for reducing hard cement clinker into powdered Portland cement: The drum of the mill was 2,2 meters in diameter, 14 meters its total length, the ball section was meters long and was subsequently reconstructed according to this invention, viz. subdivided by plane partition walls longitudinally extending through the drum and deviating from the radial direction: The output of the mill rose by while 29% less power was consumed and the temperature of the pulverulent product went down from 118 centigrade to 108 centigrade after the re-construction.

In both 'cases, viz. before and after the reconstruction the fineness of the powdered product was the same as ascertained at the laboratory of the Society of German Portland Cement Manufactures by sieving the products under comparison through a sieve of 4900 meshes.

What I claim is:

1. A grinding mill comprising a rotary drum, partition walls longitudinally extending therethrough and subdividing the drum into a plurality of grinding chambers, said partition walls tively 9,018,170. gravitaliy controlled conveying means ior con-- being plane and deviatinj from the radial di-' rection, so ts to enclose an additional chamber at the mm of the drum, andmeans cooperamaterial under treatment. said te'edin'z' means comprising partition walls. provided iii-said centrnl chamberiand subdividing the latter into a plurality of channels, perforated screensv provided in the circumierentiai wailsot central cbam- :o eommun etion o! the s'a-id' channels with iated with said grinding chambers for: ieedin'g thereinto and dischargingthereimm' the,

the individual grinding chambers, aravitslly controlled oqnveyinl means for conveying the materie-ltobegmundthroushsaidchannelsand into the grindinzchambers, and a hood structure within the latter enclosing said perioratedscreenandbeinsadsptedtosaiemm'dthe latter against beins damased.

3. Inagrindinz millarotsrydrummsrtition walls said drum into apinrslity oi non-communicating, exceiitrically located grindin: chambers, said partition wells beim substantially plane 'smi crosswisely intersectin': each other-at acuteansiesso as to jointly enclose a separate chamber at the center of the drum.

and means ior feeding into said grinding ehanris here and discharllnl thereirom thematerlai undertreatment. v 

